1. Field of the Invention
The present invention relates to a process and an apparatus for building tyres for vehicle wheels.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures integrated into the regions usually identified as “beads”.
Associated with the carcass structure is a belt structure comprising one or more belt layers, arranged in superposed relationship with each other and the carcass ply and provided with textile or metallic reinforcing cords having a crossed orientation and/or being substantially parallel to the circumferential extension direction of the tyre.
A tread band of elastomeric material, like other semifinished products constituting the tyre, is applied to the belt structure at a radially external position.
In addition, at an axially external position, respective sidewalls of elastomeric material are applied to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
After building of the green tyre through assembly of the respective semifinished products, a curing and moulding treatment is generally carried out which aims at determining the structural stabilisation of the tyre by cross-linking of the elastomeric material, as well as impressing the tread band with a desired tread pattern and stamping possible distinctive graphic signs on the sidewalls.
Within the scope of the present invention and in the following claims, by “elastomeric material” it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this composition further comprises additives such as cross-linking agents and/or plasticizers. Due to the presence of the cross-linking agents, this material can be cross-linked by heating, so as to form the final article of manufacture.
To the aims of the present description and the following claims, by “strip-like element” it is intended an elongated article of manufacture cut to size which has a cross-section profile of flattened conformation and comprises one or more cords of textile and/or metallic material, extending parallel to the longitudinal extension of the strip-like element itself and embedded into or at least partly coated with at least one layer of elastomeric material.
Document WO 01/38077, in the name of the same Applicant, discloses a method and an apparatus for production of a belt structure of a tyre for vehicle wheels. The belt structure is built using strip-like elements laid down in circumferential sequence and in mutually approached relationship on a toroidal support. The apparatus contemplates the presence of a laying unit comprising two presser elements, each carried by a support element movable along a guide structure, upon the action of transverse-actuation devices, in a substantially axial direction of the toroidal support. Each presser element is movable along the strip-like element, exerting a counter-action against the radially external surface of the toroidal support. Also preferably in engagement with each support element is at least one auxiliary retaining element that lends itself to co-operate with the respective presser element so as to retain the strip-like element at the instants intervening between cutting of said strip-like element from a continuous ribbon and application of same onto the toroidal support.
Through movement of the support elements away from each other, a simultaneous translation of the presser elements along the strip-like element away from the equatorial plane is determined, so as to cause application of said strip-like element on the toroidal support along the whole length thereof, by a pressing action progressively extending to the opposite ends of the strip-like element starting from the central portion.
Document WO 2009/068939 in the name of the same Applicant discloses a method of building a carcass ply on a forming drum. The carcass ply is made using building devices intended for application of a plurality of strip-like elements in circumferential mutual-contact relationship with each other on the forming drum, so as to form at least one ply layer having a continuous circumferential extension around the geometric axis of said forming drum, in the same manner as described above for building of the belt structure on the toroidal support with reference to document WO 01/38077.
Document EP 0 956 940 discloses a method and an apparatus for making a reinforcing layer of a tyre on the outer peripheral surface of a rigid support. Ribbon sections, each comprising parallel steel cords covered with rubber, are attached in succession onto the outer peripheral surface of the rigid support along a circumferential direction, with the side edges of the ribbon sections in contact with the edges of the adjacent sections. The sections are carried and applied onto the rigid support by the arms of industrial robots provided with magnetic bodies at their ends, which bodies are able to retain said sections as they include the aforesaid steel cords.